1. Field of Invention
The present invention relates to ship design in general and in particular to a ship hull having increased longitudinal strength by means of a structure external to the hull.
2. Description of Related Art
Shipping goods and materials is a common and efficient method of distributing such materials around countries and the globe. In particular for use on rivers and inland waterways barges and similarly designed powered vessels are commonly used. Such shipping requires the use of marine vessels adapted to carry an adequate amount of material to make the shipping process economical. Additionally, the vessels required for such shipping need to be sufficiently strong to support cargo, resist external loads and ensure safety of navigation.
One measure of hull strength is the hull section modulus which is a measure of geometric stiffness (expressed in length unit to third power, e.g. cu ft or m3). Marine vessels are traditionally required to have a minimum hull section modulus in order to provide adequate longitudinal strength that will prevent the hull from breaking.
As illustrated in FIGS. 1 and 2, a prior art container ship for use in inland waterways is illustrated generally at 10 comprising a hull 12, a main deck 14 located thereabove with a plurality of containers 8 located above the main deck. Such vessels commonly include a solid deck for reasons of economy of construction. Accordingly, such vessels only receive and transport containers upon the top deck surface. Longitudinal strength in such vessels is commonly achieved by increasing the size and strength of the longitudinal structural members of the vessel such as the bottom shell and the deck as well as introducing longitudinal beams 16 therealong which are used to stiffen them.
However such approach of adding additional or thicker members for the hull or deck increases the weight of the vessel thereby limiting the cargo which may be carried thereby and increasing both the cost of the vessel to construct and operate.
An additional means of longitudinally stiffening marine vessels is to increase hull depth, or the height of the deck above the bottom of the hull shell. A disadvantage of such raised deck heights in inland waterway vessels is that any shipping containers which are located thereupon are also raised thereby limiting the number of such containers which may be carried on such a vessel that is intended to pass under bridges and the like.